Coating aluminum

[Lou]

What is the best product to use to coat aluminum before I bolt it to
the wood on my spars?
Lou

[Orval Fairbairn]

In article . com>,
"Lou" > wrote:

> What is the best product to use to coat aluminum before I bolt it to
> the wood on my spars?
> Lou

Alodine + 2-part epoxy primer.

--
Remve "_" from email to reply to me personally.

[Lou]

Ok, but why do I want to coat the aluminum? Is this a process just for
metal planes?
should i be doing this on my aluminum hinges attatched to my wooden
spars?
Lou

[Smitty Two]

In article >,
"Morgans" > wrote:

> "Lou" > wrote in message
> oups.com...
> > Ok, but why do I want to coat the aluminum? Is this a process just for
> > metal planes?
> > should i be doing this on my aluminum hinges attatched to my wooden
> > spars?
> >
>
> Aluminum will oxidize if left to it's own means. What the etch - alodine
> coat process does is prevent the process form continuing on it's own.
>

Aluminum protects itself. When it rusts (aka oxidizes,) which it does
very very quickly, it forms aluminum oxide (duh.) A coating of aluminum
oxide is about the hardest, most impervious thing you could put on a
piece of metal. The "process" does not "continue on its own." As soon as
a microscopically thin layer forms, your aluminum is protected from
further degradation.

The problem arises when the exposed metal is left to water, salts,
dissimilar metals, etc, for long periods of time, which sets up
electrolysis. If you think you're going to protect aluminum from that
kind of damage with some kind of coating, then be my guest. I plan to
keep my plane clean and dry, and let the aluminum oxide that forms
naturally do its job.

Now, I know Mr. Morgans isn't going to flame me for these comments,
because he's already canned me, but I'd love to hear from others who may
disagree.

Jon in California

[Morgans]

"Lou" > wrote in message
oups.com...
> Ok, but why do I want to coat the aluminum? Is this a process just for
> metal planes?
> should i be doing this on my aluminum hinges attatched to my wooden
> spars?
>

Aluminum will oxidize if left to it's own means. What the etch - alodine
coat process does is prevent the process form continuing on it's own.

Etch- remove oxidation, and roughen the surface (chemically) to make bonding
of new coatings stronger.

Alodine- actually cause a very uniform thin layer of oxidation to form on
the aluminum, that will help the oxidation from continuing on its own, in
un-uniform ways, possibly up to and including consuming the base metal.
Oxidation on the surface actually protects the metal under it.

Coat- Protects the layer of alodine from wearing away, or continuing on its
own, due to contact to other unlike surfaces, or exposure to the
environment. 2 part epoxies are the best (in some (most) people's opinions)
because it is very resistant to chemicals, moisture, and friction of rubbing
against another surfaces. It also has very good adhesion properties,
allowing it to stick to surfaces and not let go.
--
Jim in NC

[Roger]

On Wed, 14 Dec 2005 21:11:09 -0800, Smitty Two
> wrote:

>In article >,
> "Morgans" > wrote:
>
>> "Lou" > wrote in message
>> oups.com...
>> > Ok, but why do I want to coat the aluminum? Is this a process just for
>> > metal planes?
>> > should i be doing this on my aluminum hinges attatched to my wooden
>> > spars?
>> >
Ok,I'm no expert on painting, but I'll take both sides here
>>
>> Aluminum will oxidize if left to it's own means. What the etch - alodine

Wellll, yah, kinda, sorta, but...It really depends on to what it's
exposed.

>> coat process does is prevent the process form continuing on it's own.
>>
Alodine is pretty fragile and the Aluminum Oxide is pretty tough.
Unfortunately both have their weaknesses.
>
>Aluminum protects itself. When it rusts (aka oxidizes,) which it does
>very very quickly, it forms aluminum oxide (duh.) A coating of aluminum

It forms that layer which is only a few molecules thick almost
instantly.

>oxide is about the hardest, most impervious thing you could put on a
>piece of metal. The "process" does not "continue on its own." As soon as
>a microscopically thin layer forms, your aluminum is protected from
>further degradation.

Within reason I agree such as just leaving it alone

>
>The problem arises when the exposed metal is left to water, salts,
>dissimilar metals, etc, for long periods of time, which sets up

When it comes to salts it doesn't take much time. Look at the
corrosion around the joints on paint jobs with poor prep.

>electrolysis. If you think you're going to protect aluminum from that
>kind of damage with some kind of coating, then be my guest. I plan to
>keep my plane clean and dry, and let the aluminum oxide that forms
>naturally do its job.
>
>Now, I know Mr. Morgans isn't going to flame me for these comments,
>because he's already canned me, but I'd love to hear from others who may
>disagree.

The Alodine process does two things. It is a prep for painting so it
gives the paint a surface to which it can grip really well.

Alodine itself is relatively fragile. It is very thin and can be
rubbed off, but between the added protection against dissimilar metals
and a good surface for your paint to stick to, I think it's worth the
effort. Give it a good primer and your paint job should last a long
time.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
>
>Jon in California

[RV9]

> Aluminum protects itself. When it rusts (aka oxidizes,) which it does
> very very quickly, it forms aluminum oxide (duh.) A coating of aluminum
> oxide is about the hardest, most impervious thing you could put on a
> piece of metal. The "process" does not "continue on its own." As soon as
> a microscopically thin layer forms, your aluminum is protected from
> further degradation.

I'm no expert, however my understanding is...

6061 and 2024 are not pure aluminum. In order to obtain the desired strength
properties, other metals are added to the aluminum. I believe 2024 has
something of the order of a couple percent of copper. The surface will not
be pure aluminum oxide, since there are "impurities" within the metal. You
are now open to pitting corrosion as well as granular corrosion.

The alodine forms a passivated layer, that uniformly protects the whole
surface. Being a delicate surface itself (as a previous poster already
mentioned), the passivated layer needs to be protected against mechanical
abrasion.

6061 is quite immune to most of the above corrosion. It is still a good idea
to protect anywhere you will have metal to metal contact though, since you
can have moisture trapped between the parts which accelerates the corrosion.

I use 2024, so I do the scuff, etch, alodine, 2 part epoxy prime routine.

[Morgans]

"RV9" > wrote

> I'm no expert, however my understanding is...

Obviously your understanding is far above Smitty's

> I use 2024, so I do the scuff, etch, alodine, 2 part epoxy prime routine.

As would any sensible person working aluminum in an aircraft.

Strange, isn't it, that the Navy (and I suspect the other armed forces)
spend all of that time with the above procedure on their aircraft? They
must know something that Smitty does not.
--
Jim in NC

[Capt. Geoffrey Thorpe]

> 6061 and 2024 are not pure aluminum. In order to obtain the desired
> strength
> properties, other metals are added to the aluminum. I believe 2024 has
> something of the order of a couple percent of copper. The surface will not
> be pure aluminum oxide, since there are "impurities" within the metal. You
> are now open to pitting corrosion as well as granular corrosion.
>

2024

Cu 3.8 - 4.9
Mg 1.2 - 1.8
Mn 0.30 - 0.9
Fe <= 0.50
Si <= 0.50
Zn <= 0.25
Zr+Ti <= 0.20
Total Other <= 0.15
Ti <= 0.15
Cr <= 0.10
Other Elem <= 0.05
Al Remainder



6061

Mg 0.40 - 0.8
Si 0.30 - 0.6
Fe <= 0.35
Cu <= 0.25
Cr <= 0.20
Mn 0.05 -0.20
Total Other <= 0.15
Zn <= 0.15
Ti <= 0.10
Other Elem <= 0.05
Al Remainder

All compositions in wt%.

"alclad" sheets have a thin layer of pure aluminium on the surface to
improve corrosion resistance.

see http://aluminium.matter.org.uk/aluselect/02_corrosion_browse.asp for
corrosion and anodizing properties.


--
Geoff
the sea hawk at wow way d0t com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

[Ernest Christley]

Smitty Two wrote:
> In article >,
> "Morgans" > wrote:
>
>
>>"Lou" > wrote in message
oups.com...
>>
>>>Ok, but why do I want to coat the aluminum? Is this a process just for
>>>metal planes?
>>>should i be doing this on my aluminum hinges attatched to my wooden
>>>spars?
>>>
>>
>>Aluminum will oxidize if left to it's own means. What the etch - alodine
>>coat process does is prevent the process form continuing on it's own.
>>
>
>
> Aluminum protects itself. When it rusts (aka oxidizes,) which it does
> very very quickly, it forms aluminum oxide (duh.) A coating of aluminum
> oxide is about the hardest, most impervious thing you could put on a
> piece of metal. The "process" does not "continue on its own." As soon as
> a microscopically thin layer forms, your aluminum is protected from
> further degradation.
>

Bingo! You are 100% correct Smitty. The oxide is impervious to water
and is very resisant to abrasion. Many metals form an insoluable oxide,
with the most notable exception being steel. Rust is soluable AND
hygroscopic, so the rust just goes straight through once it starts.

The wild card here is acid. Acid will eat right through the oxide layer
without stopping to ask questions, exposing another microscopic layer,
which then oxidizes. Unfortunately, our culture has spent the last
200years burning tons of coal and dumping all sorts of sulfur in the
air. This sulfur rains back down on us (and our airplanes) as very
dilute sulfuric ACID. That's why the Statue of Liberty needed to be
refubished. The acid rain had worn the copper thin.

Put something on that aluminum, not to protect it from water which is
actually rather benign to aluminum for the reason you state, but to
protect it from the acid that you'll be flying through.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

[Lou]

Ernest Christley wrote:
> Smitty Two wrote:
> > In article >,
> > "Morgans" > wrote:
> >
> >
> >>"Lou" > wrote in message
> oups.com...
> >>
> >>>Ok, but why do I want to coat the aluminum? Is this a process just for
> >>>metal planes?
> >>>should i be doing this on my aluminum hinges attatched to my wooden
> >>>spars?
> >>>
> >>
> >>Aluminum will oxidize if left to it's own means. What the etch - alodine
> >>coat process does is prevent the process form continuing on it's own.
> >>
> >
> >
> > Aluminum protects itself. When it rusts (aka oxidizes,) which it does
> > very very quickly, it forms aluminum oxide (duh.) A coating of aluminum
> > oxide is about the hardest, most impervious thing you could put on a
> > piece of metal. The "process" does not "continue on its own." As soon as
> > a microscopically thin layer forms, your aluminum is protected from
> > further degradation.
> >
>
> Bingo! You are 100% correct Smitty. The oxide is impervious to water
> and is very resisant to abrasion. Many metals form an insoluable oxide,
> with the most notable exception being steel. Rust is soluable AND
> hygroscopic, so the rust just goes straight through once it starts.
>
> The wild card here is acid. Acid will eat right through the oxide layer
> without stopping to ask questions, exposing another microscopic layer,
> which then oxidizes. Unfortunately, our culture has spent the last
> 200years burning tons of coal and dumping all sorts of sulfur in the
> air. This sulfur rains back down on us (and our airplanes) as very
> dilute sulfuric ACID. That's why the Statue of Liberty needed to be
> refubished. The acid rain had worn the copper thin.
>
> Put something on that aluminum, not to protect it from water which is
> actually rather benign to aluminum for the reason you state, but to
> protect it from the acid that you'll be flying through.
>
> --
> This is by far the hardest lesson about freedom. It goes against
> instinct, and morality, to just sit back and watch people make
> mistakes. We want to help them, which means control them and their
> decisions, but in doing so we actually hurt them (and ourselves)."


Ok, but why alodine, why not rustolium?

Lou

[Morgans]

"Lou" > wrote

> Ok, but why alodine, why not rustolium?

Why? Two reasons.

1. Rustoleum sucks
2. If you put regular ole paint on Aluminum without prep to remove the
oxides, and promote a solid bond, you can scratch off regular paint with
your fingernail.
--
Jim in NC

[Cy Galley]

One of the basic reasons to protect aluminum as unprotected it will develop
Intergranular Corrosion mainly because of the copper in the alloy.


"Lou" > wrote in message
oups.com...
> Ok, but why do I want to coat the aluminum? Is this a process just for
> metal planes?
> should i be doing this on my aluminum hinges attatched to my wooden
> spars?
> Lou
>

[Ernest Christley]

Lou wrote:
> Ernest Christley wrote:
>
>>Smitty Two wrote:
>>>Aluminum protects itself. When it rusts (aka oxidizes,) which it does
>>>very very quickly, it forms aluminum oxide (duh.) A coating of aluminum
>>>oxide is about the hardest, most impervious thing you could put on a
>>>piece of metal.

>>Bingo! You are 100% correct Smitty. The oxide is impervious to water
>>and is very resisant to abrasion. Many metals form an insoluable oxide,
>>with the most notable exception being steel. Rust is soluable AND
>>hygroscopic, so the rust just goes straight through once it starts.
>>

>
> Ok, but why alodine, why not rustolium?
>
> Lou
>

Because, exactly as Smitty wrote, ALUMINUM PROTECTS ITSELF. Not just
from water, but also from paint.

That protection is very hard just like he said and reforms very quickly
in the presence of oxygen after being removed. The purpose of the
alodine is to chemically 'scratch' up the surface in such a way that
paint is able to form a mechanical bond.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

[[email protected]]

Ernest Christley wrote:
>
> ...
>
> The wild card here is acid. Acid will eat right through the oxide layer
> without stopping to ask questions, exposing another microscopic layer,
> which then oxidizes. ...

The other wild card is casutics (bases). Aluminum is equally
susceptible
to caustics. Lye (sodium hydroxide) will react as violently (or even
more so)
as does sulphuric acid.

--

FF

[RV9]

> The other wild card is casutics (bases). Aluminum is equally
> susceptible
> to caustics. Lye (sodium hydroxide) will react as violently (or even
> more so)
> as does sulphuric acid.

Tell me about it. I used dish soap when checking for fuel tank leaks
(unprimed tanks on a homebuilt project). Result was some mild corrosion
anywhere the aluminum had a scratch on it (2020 coated with 1 mil of pure
aluminum). It'll come off when I prepare the surface for painting (lots of
scuffing with 300 grit).

I had picked up a dish soap bottle from under the sink, and unfortunately it
was not Dawn (some people recommend Dawn due to low causticity, and I have
used Dawn successfully in the past as well).

My motto for 2024... scuff, etch, alodine, prime.

[Lou]

So, let me get this right,
acid bad
Alodine good.

[RV9]

> So, let me get this right,
> acid bad
> Alodine good.
>

Except when you use the acid to etch the aluminum before alodining it :-)
Shouldn't over-etch either (about 3 minutes in dilute acid solution).

2024 is protected by pure aluminun, but the coating is so thin and delicate,
that you are bound to put scratches in it. For 6061, at the very least,
prime on faying surfaces.

[Lou]

Thanks everyone, I'll be ordering the solution this week.
Lou

[.Blueskies.]

"Lou" > wrote in message oups.com...
> So, let me get this right,
> acid bad
> Alodine good.
>

Alodine is acid - chromic acid.

[Morgans]

".Blueskies." > wrote in message
om...
>
> "Lou" > wrote in message
oups.com...
> > So, let me get this right,
> > acid bad
> > Alodine good.
> >
>
> Alodine is acid - chromic acid.

Now that I didn't know...or had forgotten!
--
Jim in NC

[Morgans]

"Lou" > wrote in message
oups.com...
> Thanks everyone, I'll be ordering the solution this week.

Good choice. Alodine treatment is the clear cut industry standard.

It is interesting to hear about the Navy's anti corrosion cycle. Given,
they operate airplanes in some of the harshest environments in the world.

A good friend of mine was a Master Chief in the Navy, working on aircraft
from Vikings to A-6's, to FA-18's. Another note of interest is that he
never served on a nuclear carrier. They had?have (how many now, I don't
know, anyone else know?) a lot of conventional carriers out there, even
though all you hear about are the Nukes. The conventional carriers add
another negative impact on the maintenance of the aircraft. The fuel burned
for propulsion is an added factor accelerating corrosion.

Airplanes are regularly taken out of service, and either areas, or the whole
airplane is completely stripped down, and the parts are stripped, retreated
and reassembled. If they did not do this, I'm quite sure that their
airplanes would indeed start falling out of the air.
--
Jim in NC

[[email protected]]

>> Alodine is acid - chromic acid.

>Now that I didn't know...or had forgotten

And the acid etch applied before alodining to remove any
corrosion products is phosphoric acid.
Aluminum is never found in the free state as many other metals
sometimes might be. And it doesn't smelt easily, requiring huge amounts
of electricity to electrolyze it out of the ore. So it's a relatively
recent metal, being rather scarce (and super-expensive) 100 years ago,
in spite of the fact that it's one of the most abundant elements in the
earth's crust.
I suppose we don't find it in its free state in nature because
it reacts so easily with just about anything else and returns to its
former oxides or sulphates or chlorides or whatever. And I imagine
that's why it hasn't seen wide service in cars, what with all the road
salt used in many areas. Even inside an airplane wing we find surface
corrosion on uncoated 2024, just from condensation. Any good floatplane
will have its interior zinc-chromated.

Dan

[Ernest Christley]

..Blueskies. wrote:
> "Lou" > wrote in message oups.com...
>
>>So, let me get this right,
>>acid bad
>>Alodine good.
>>
>
>
> Alodine is acid - chromic acid.
>
>

I hear the confusion, Lou. Yes, alodine is also acid, but what your
doing is using the acid in a CONTROLLED environment. You put the piece
in the alodine bath for only a short time. Leaving it there for
extended periods IS bad. It'll eat your part up.

After you get the surface coated with a good layer of whatever chromium
compound it is that the alodine leaves behind, you pull it out of the
solution and wash it with clean water. As soon as it is good and dry,
you put a coat of primer on it.

The post about bases is spot on, except that you don't find them in the
air much. Most of the acid in the rain is put there either by burning
coal or diesel fuel. As Morgans pointed out, the air around diesel
driven air carriers has given the Navy fits for decades.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."